1. Field of the Invention
The invention relates to a ventilator circuit for use with a low pressure low flow oxygen generator that by design requires less oxygen to achieve a desired oxyhemoglobin percentage at the patient as compared to conventional means of oxygen delivery.
2. Description of the Related Art
The respiratory and/or circulatory systems of many patients may not be sufficiently viable to sustain the patient with oxygen levels that exist in ambient air. A typical ventilator system contains a means to deliver ambient or compressed air to a patient. The ventilator typically has means to accept oxygen from a high pressure or low pressure source and to vary the mixture of air and oxygen. A ventilator circuit communicates with the ventilator and the patient. The ventilator circuit provides a conduit for the gas or gas mixture to be delivered cyclically to the patient and then to be exhaled by the patient. The ability to have high pressure oxygen available in sufficient volume is not always possible or practical. In most hospitals, liquid oxygen is converted to a gas, pressurized, and made available via a piped system to wall outlets located throughout the facility. This source of oxygen supply is plentiful and generally is available at all times unless there is a power failure or generating system failure. Hospitals maintain a limited supply of oxygen that is stored in cylinders for intra-hospital transport and backup use in the event that the primary system fails. High pressure oxygen that is stored in cylinders is delivered through a pressure reducing regulator. When full, the cylinder stores compressed oxygen at about 2200 PSI. Cylinders are available in various sizes, and the size determines the oxygen storage volume and the degree of portability. The cylinder size can impose handling constraints on the caregiver and mobility constraints on the patient. Reliance on oxygen cylinders also can present a risk if resupply is not available. Accordingly, oxygen generators may be considered an alternative way to provide higher concentrations of oxygen. A ventilator circuit is required to provide communication between the ventilator and the patient and acts as a conduit for the gas or the gas mixture to be delivered to the patient and then exhaled by the patient. Low pressure low flow oxygen generators are sufficient for many applications and often are the only practical alternative. Examples of low pressure low flow oxygen generators include oxygen concentrators, chemical oxygen generators, oxygen therapy regulators connected to a nominal 50 PSI source and ceramic oxygen generators. Oxygen concentrators can rely upon positive pressure swing adsorption or positive/negative pressure swing adsorption. Chemical oxygen generators can be solid generators or solid/liquid generators. Some oxygen generators can be controlled to cycle “on” and “off” as needed. Other oxygen generators, once activated, remain “on” until their chemical reaction is exhausted.
Low pressure/low flow oxygen generators typically have an output of less than 10 liters per minute with five-six liters per minute being the most common.
The typical prior art ventilator circuit, by design, is incompatible for direct use with oxygen enrichment devices. Instead, oxygen is mixed with air or is delivered unmixed by the ventilator and through the ventilator circuit to the patient in a sufficient volume to meet the needs of the patient. Another less common method is to direct a continuous low flow rate of oxygen to a reservoir that communicates with the compressor intake of a ventilator. The ventilator cycles “on” to deliver a breath via the ventilator circuit. As a result, the reservoir content is delivered to the patient along with supplemental air if needed. In the former example, the oxygen percentage is set at the ventilator and delivered to the patient via the ventilator circuit. In the latter example, the percentage to be delivered is measured by an oxygen monitor at the connection between the output of the ventilator and the input of the ventilator circuit. Adjustments to the oxygen flow rate into the reservoir are made until the desired mixture is being sent from the ventilator to the patient. The typical prior art ventilator circuit permits inspiration gas to be delivered to the patient and exhaled gas to be conducted away from the patient. This inflow and outflow of gas is embodied in ventilator circuits that have single limb, dual limb and coaxial designs. The circuit includes a patient connection that is configured for connection with a mask or endotracheal tube that will be placed directly in communication with the patient.
In use, the patient will inhale the oxygen rich gas that flows through the ventilator circuit. The patient then will exhale and the exhaled gas will flow mostly through the ventilator circuit and out the exhalation valve. The exhalation valve is either part of the ventilator circuit or part of the ventilator, depending on whether the circuit design is a single limb, a dual limb or coaxial. A portion of the exhaled gases, including carbon dioxide, will remain in the ventilator circuit. As a result, the next inspiration cycle will start with that portion of the remaining gases, including the carbon dioxide being delivered to the patient. Accordingly, the oxygenation process will exhibit less than optimum efficiencies, and it may be necessary to provide a higher percentage of oxygen with each successive breath to compensate for the remaining gases of the previous breath. This can quickly deplete a limited supply of oxygen.
A system that could control the appropriate flow of oxygen to a patient would achieve several significant advantages. For example, approximately one-third of the volume of gas that is delivered to the patient never gets to the lungs distal alveoli because it never gets past the upper respiratory tract area. This area generally is known as “dead space” where no gas exchange takes place. Thus, a ventilator circuit that is capable of prefilling itself with a higher concentration of oxygen to be delivered at the front end of a breath and ambient air at its back end will ensure (i) that a higher concentration of oxygen will reach the distal alveoli, (ii) that mostly ambient air will wind up in the dead space area, and (iii) the use of less oxygen, by volume, can provide effective oxygenation equivalent to that of a greater volume of oxygen used in a conventional manner. In yet another example, the oxygen generator could be smaller, or for any given size, the oxygen generator could require replacement or maintenance less frequently due to a lower demand on its output capability. Accordingly, it is an object of the subject invention to provide a ventilator circuit that can be used with a ventilator and a low pressure low flow oxygen generator to provide more efficient use of the oxygen generator.